Method of making gears



E. E. lARNOLD METHOD OF MAKING GEARS Filed April 11, '192s 2 Sheets-Sheet l INVENTOR Ed n E.Arno1d A ONEY Oct. 20, 1931. E. E. ARNOLD METHOD OF MAKING GEARS Filed April 1l. 1929 2 Sheets-Sheet 2 mvENToR Edwin EA? nold ATfoRNEY Patented Oct. 20, 1931 UNITED STATES PATENT oFFlcE EDWIN E. ARNOLD,

OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WETINGHOUSE i ELECTRIC MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA IETHOD OF MAKING GEABS f Application led April 11,

i' i@ a relatively high coefficient oi expansion united, by a casting or molding operation, to an inner web or hub formed of a metal or alioy having a rela-tively low coeiiicient of expansion.;

Another object of Imy' invention is to provide a method of uniting an outer rim or seg ment of a machine element to an inner web or hub by a casting or molding operation:

A further object of my invention is to pro- 2@ vide a method of integrally uniting an outer riin com osed ci a relatively expensive metal or alloy aving a comparatively high coeiicient ci expansion, such as bronze, to a centrai web or hub composed oi a satisfactory i metal or alloy, having a comparatively low coetlicient et expansion which is inexpensive, such as cast iron, by a casting or molding operation which comprises heating'the bronze in a mold and then pouring suiicient molten iron to form the central hub and web internally of the rim, the heat imparted to the rim expanding it to such extent that, during the con raction of the parts, the outer rim, because of its greater rate of contraction, will be shrunk, in a tight engaging t, upon the central portion.

it is customary, in making gears or gear seents which are subjected to pressure in service, such 'as worm gears utlllzed in elevators, to form the central portion of the Wear ot an inexpensive metal, such ascast iron and thel outer portion or rim of a copper-oase alloy havin bearing qualities to reduce friction and o suicient strength to resist the stresses to which the gear is subiected in service. Heretofore, 1n -making ears of this type, it has been the practice'to rst form the central portion of the gear of cast iron and machine its outer surface. The

v w inner surface of a bronze rim ie next ina-- tool, in the usual manner. from which a gear or pulley 1929. Serial No. 354,302.

hined to fit the machined surface of the castiron center, after which it is placed over, and bolted to, the cast-iron central portion. The outer surface of the bronze rin is then machined, and the teeth are cut y a hobbing This process of securing the bronze ring to `the cast-iron center is expensive because of the many machining operations required. In

view of this expensive procedure, it has been proposed to unite the cast-iron center to the ronze ring by a Welding peration but such recess also requires some machining to which is added the expense of welding. ln making machine element of the ty e specied, l have made the discovery that t e expensive machining operations may be avoided by casting the central portion interiori or a bronze iiim which has been so exande b a previods heat application, that., uring t e subsequent cooling of the cast center and the rim, the rate of contraction of the rim will exceed the rate of contraction of the central portion by a sucient degree to ensure a tight engaging fit between the two members.

My invention will be better understood by reference to the accompanying drawings o which:

Figure 1 is a cross sectial view of a sand mold showing a previously prepared bronze rim. in cross sectionand gates throu h which molten metal for forming the cast-iron center and the outer heating ring may be poured Fig. 2 is a similar view showing the bronze rim and the outer heating ring in cross section;

Fig. 3 is a cross sectional view of a complete gear or pulley blank made in accord: ance with my improved process, the outer heating ring aving been removed; v

Fig. 4 is a plan view of a segmental r blank, with theA outer heating ring in p ace and showing a passageway leading to the i center and a pluralityl of passageways leadin from the gate to e heating ring;

ig. 5 is a. cross-sectional view of a sand` mold in'which the segmental gear shown in 4 may be formed;

ig. 6 is a planview ofthe bronze rim emploled in making the segmental gear shown in ig. 4,

Fig. 7 is a detail cross-sectional view of a typical bronze ring or se'ment;

ig. 8 is a similar view s owing a modified cross section of a bronze ring;

Fig. 9 is a plan view of-the gear blank shown in Fig. 3, with the heating ring in place; and

Fi 10 is a cross-sectional view of the comp ete gear having machined teeth.

Referring to Figs. 1 and 2 of the drawings, the sand mold consists of the usual drag 1 and cope 2 in which a mold cavity 3 is formed having the shape of the complete gear blank and outside heatin rin a core 4 being inserted in the centra port-ion to form the axial opening for a suitable bearing.

In practicing my invention, a previously pre ared bronze ring 5 is first placed in the Molten iron 1s then oured through the gate 6 and flows throug the conduit 7 into the chamber 15, which extends around the exterior surface of the bronze ring 5. It is sometimes desirable to provide conduit 7 with branches 8 and 9, as shown in Figs. 4

v and 9, thereby permitting the molten metal to flow simultaneously into different portions of the annular chamber. Although either method may be utilized, the latter is preferred because it prevents undue heating or local melting of the bronze ring. After a short interval of time, say from 3 to 15 minutes, according to the size of the bronze ring and the volume of the chamber, molten iron is poured through gate 10 to form the metal center 11 which ma consist only of a hub, or of a hub and a we as shown in the drawlma beformed.'

he interval of time between which the molten metal is poured into the different portions of the mold permits the metal in chamber 15 to form aheating ring 12 which transfers a portion of its heat to the bronzering 5. Heat is also transferred to the bronze rin from the metal which forms the cast centra portion of the gear blank. The heat thus imparted to the bronze ring causes it to expand and enlarges the portion of the mold in which the central portion is formed.

The metal portions of the gear blank and the-heating ring are then permitted to cool, during which period a Vcontraction of the elements takes place. The bronze ring, however, has a hi her rate of contraction than 'the cast centr portion so that, during the cooling process, it is shrunk to form a tight engaging fit on the cast-metal center. The heating ring 12, having a. slower rate of contraction than the bronze ring 5, may be easily removed from the latter, and a blank is thus produced from which gears or pulleys my early experimental work, it was thought that the metal which was poured into tight fit between these two mein the mold to form the cast center would supply enough heat to the bronze rin so that, during the subsequent cooling of t e center and rim, there would be suiiicient contraction of the ring, in excess of the contraction of the central portion, to cause a tight lit be tween the two elements. In practice, however, it was found that such method did not supply sufficient heat to the bronze ring so that, in the subsequent coolin process, a rs was not obtained. I then conceived the idea of sup` plying additional heat to the bronze ring. This was accompli-shed by providing the exterior chamber 15 in the mold into which molten iron is poured throu h the ate 6. Initial heat was thus supplie to the ronze ring which started its expansion prior to the pouring of the center hub portion so that, during subsequent cooling of the cast-iron center and bronze ring, a tight engaging fit between the two elements was ensured.

The following specific example will serve to illustrate and explain my invention, although it will be understood that I do not desire to limit in self to the particular features described t erein. A reviously prepared bronze ring, providedp with an interior anchoring tin 14, and having an exterior.' diameter of approximately 14% inches and an approximate cross section of 2 2 square inches, was placed in a proper y shaped mold cavity having an exterior annular chamber 15, as shown in Fi 1. The chamber 15 had a depth of 2 inc es and a radial diameter of 1% inches. During varions trials with molds of the description specified, molten iron was poured through gate 6 into chamber 15 at a temperature of 2300 to2350 F. and, after an interval of from 10 to 11 minutes, iron for the central portion was ured through ate 10 at a temperature of 23 0 to 2380 F. he entire structure was then permitted to cool and, in each case, upon removing the casting from the mold, it

, was found that the heating rin 12had cracked and could be easily remove and that the bronze rin had contracted sufficiently during the ooo ing process, to make a strong fittin engagement with the cast-metal center an to all intents and purposes, formed an inte al art thereof.

e a ve example indicates that reasonable latitude may be permitted in commercial v operations. There are three factors, however, that must be taken into consideration; namely, the volume of the heating ring, the temperature at which the metal is poured and the time which is ermitted to elapse between the pouring oftlle heating rinP and the pourin of the central portion. in lete contro of the process maybe obtained y a pro r re lation ofthese variables so that a pro uct o any desired size may be reduced My invention may also be utilize in making segmental gears, as shown in Figs. 4, 5,

and 6. In such cases, a bronze ring 5 havinghook-shape lianges 13 at each end is first placed in a mold cavity having 'the shape and vsize of the completed segment and heating ring. The iron for the heating ring is then poured, in the same manner as previously described, and, after suicient heat has been imparted to the bronze ring, the metal for the center portion is poured. As in the previous example, it is necessary that the amount of heat imparted to the bronze ring by the heating rin and by the cast-metal portion shall be suc that, during the subsequent cooling of these elements, the contraction of the bronze ring shall be suiciently in excess of the contraction of the cast-metal cenler to make a tight engaging it therewit After the blank has been formed, teeth may be cut therein to form a gear, as shown in Fig. 10 or it may be otherwise machinedto form the desired machine element.

While I have described my invention in con sidera-ble detail, it will be understood that various modifications may be made therein without departing from the spirit of my invention vand this is especially true with respect to the volume of the heating ring, the temperature at which the metal for the heating ring and that for the central portion are pour-ed, and the time. which is permitted to elapse between the pouring of the heating ring and thecentral portion, as these factors are dependent upon each other. For example,

more heat will be imparted to the bronze rim by a heating ring having a greater volume and the same is true if the metal for this ring is poured at a higlher temperature. It is, therefore. apparent t at, if the metal for the heating ring is poured at a higher temperature, the volume of the ring need not be so great. It will also be understood that, if aI larger heating ring is utilized and the metal thereforisg poured at a high temperature, it will not require as much time to vimpart a given amount of heat to the bronze ring as if either one or both of these factors are decreased. Since the metal for the cast center also imparts some heat to the bronze ring, the temperature at which the metal for this portion' of a gear blank is poured, must also be taken into consideration in the process. I have found, however, that under ordinary ey-iron-foundry conditions, good results may be obtained when the heating ring is of substantially the same section as the bronze rim and an interval of approximately 8 to 11 minutes is permitted to elapse between the pouring ofthe metal for the heating ring and the pouriiig of the metal for the cast center'. Other iiodiications of my invention will also be apparent to those skilled in the art.

For example, the 'iin 10 ofthe bronze ringv may be made in any one of .various shapes, an

illustration being shown at .14 in Fig. 8. The

bronze ring may also be provided with notches, as shown at 12 in Fig. 9,' to insure a perfect junction between the cast iron center and the rim. I desire, therefore, that only such limitations shall be imposed upon my invention as are required by the prior art and the appended claims.

I claim as my invention:

l. The method of manufacturing gear blanks which comprises placing a rim composed of an alloy having a comparatively high coeicient of expansion in a mold to divide the cavity of the mold into an outer annular chamber and an inner chamber, causing said rim to expand by means Iof molten metal supplied to said outer chamber, pouring molten metal having a. comparatively low coefficient of expansion into .the central chamber, such heat being supplied to said rim by means of the molten metal that, during the cooling of the blank, there will be a suiicient contraction of the rim in excess of the contraction of the central portion to insure a tight engaging t between the two members.

2: The method of manufacturing gear blanks which comprises placing a bronze rim having an inwardly extending annular fm in a mold to divide the mold cavity into an outer annular chamber and an inner chamber, eX- panding said rim by means ofl heat imparted to it by pouring molten metal into the outer chamber, pouring molten metal having a comparatively low coefficient of expansion into the inner chamber, said metal making contact with, and imparting additional heat to, said rim, the total amount of heat supplied to said rim being suicient to cause itto expand while hot so that it will have such contraction during the cooling in excess of the contraction of the central portion as to form a tight engaging fit between the two members. I

. 3. The method of producing a machine element comprising a rim having va relatively -high coefficient of expansion and a cast metal center having a comparatively low coeilicient .of expansion which comprises placing the rim in a mold, heating said rim, and pouring molten metal interiorly of the rim, thereby supplying additional heat tn the rim, the total amount of heat supplied to the rim being such that, ,during the coolin of the element, the' rim will contractt suiciently to form a tight engaging fit with the inner cast-metal portion.

4. The 'method of producing a machine element comprising two metallic portionsA having different coefficients of expansion which comprises placing the metal or alloy having the greater coeicient of expansion in a mold, heating the same and then pouring the Vmolten metal forming'the portion having the lower coefficient of expansion into the mold so as to makecontact with, and supply additional heat to, the rst mentioned'meta ius the total amount of heat supplied to the metal having the high coefficient of ex nsion being such thatit will shrink into a tight engaging fit upon the metal having the lower coeicient of expansion during the cooling of the two portions.

5. The methodof producing gear blanks which comprises placing a rim composed of a metal or an alloy having a comparatively high coeflicient of expansion in a mold, heating the rim after it has been placed in the mold, uring a metal or alloy having a lower coeilicient of expansion interiorly of the rim Vsothat it will flow in Contact with the rim and supply additional heat thereto, the total amount of heat supplied to the rim being such that, upon cooling of the rim and castmetal center, the higher rate of contraction of the rim will cause it'to make a tight engaging iit upon the cast-metal center.

6. The method of producing gear blanks which -comprises placing a bronze rim in a mold, heating said rim after it has been placed in the mold, pouring a molten ferrous metal interiorly of the bronze rim so that it will come in contact with, and supply additional heat tc` the rim, the preliminary heat supplied to said rim, being such that, together with the additional heat supplied b the molten ferrous material, the rim will be expanded sufiiciently so that, during the coolingI of the blank, the rim will contract and make a tight engaging fit on the solidified ferrous central portion.

7. The process of producing gear blanks comprising a rim and a cast central portion which comprises heating the rim, pouring lnolten metal interior-ly of the rim, thereby imparting additional heat to the rim, the'total amount of heat supplied to the rim being such that. during the coolingr of the blank, the rim will be shrunk into a tight engaging fit on the central portion.

8. In the process of producing machine i elements comprising a rim and a central portion having different coeiicients of expansion, Vthe steps which comprise heating said rim by means of molten metal poure exteriorly of said rim and then casting molten metal interiorly of said rim.

In testimony whereof, I have hereunto subscribed my name this 28th day of March, 1929.

EDWIN ENGL 

